General thermoplastic synthetic fibers such as nylon or polyester fibers melt at about 250° C. or so. However, heat-resistant high-functional fibers such as aramid fibers, holaromatic polyester fibers and polyparaphenylene-benzobisoxazole fibers do not melt at about 250° C. or so, and their decomposition temperature is about 500° C. or so and is high. The critical oxygen index of the non-heat-resistant general fibers, nylon or polyester fibers is about 20 or so, and the fibers well burn in air. However, the critical oxygen index of the heat-resistant high-functional fibers such as those mentioned above is at least about 25, and the fibers may burn in air when they are brought near to a heat source of flames, but could not continue to burn if they are moved away from the flames. To that effect, the heat-resistant high-functional fibers have excellent heat resistance and flame retardancy. Therefore, aramid fibers, a type of heat-resistant high-functional fibers are favorable to clothes for use in high risk of exposure to flames and high temperatures, for example, for fireman's clothes, racer's clothes, steelworker's clothes, welder's clothes, etc. Above all, para-aramid fibers having the advantages of heat resistance and high tenacity are much used for sportsman's clothes, working clothes, ropes, tire cords and others that are required to have high tear strength and heat resistance. In addition, as they are hardly cut with edged tools, the fibers are also used for working gloves. On the other hand, meta-aramid fibers are resistant to heat and have good weather resistance and chemical resistance, and they are used for fireman's clothes, heat-insulating filters, heat-resistant dust-collecting filters, electric insulators, etc.
Heretofore, when the heat-resistant high-functional fibers are formed into fibrous products such as clothes, they are used merely in the form of non-crimped filaments or spun yarn. However, even when such non-crimped yarn of filaments or spun yarn is worked into fabrics and formed into clothes such as fireman's clothes, racer's clothes and working clothes, the resulting clothes are poorly elastic as the yarn itself is not elastic. As a result, when the clothes are worn, they are problematic in that their feel is not good and they are unsuitable to exercises and working activities.
In particular, working gloves made of conventional non-crimped yarn are unsuitable to use in the industrial fields of airplanes, information systems and precision machines in which precision parts are handled, as they do not well fit with worker's hands. Using the gloves in those industrial fields often results in the reduction in the working efficiency. In the field of medicine, for example, in the field of surgical operations of treating AIDS cases and the like that will cause infection by blood, the surgeons wear rubber gloves or elastomer gloves (hereinafter referred to as rubber gloves) to protect themselves from the patient's blood. Ambulance men take care of unspecified, wounded or sick persons, and they wear rubber gloves to protect themselves from the blood and body fluid of patients who are not yet identified as infectious. However, rubber gloves will be readily broken by operation tools such as surgical knives, and they could not completely protect the medical and surgical workers such as physicians, surgeons and ambulance men, from surgical knives, syringe needles and others stained with patient's blood. In that situation, it may be taken into consideration to wear woven or knitted gloves of heat-resistant high-functional fibers with high mechanical strength such as those mentioned above, inside rubber gloves. However, as mentioned hereinabove, the conventional gloves of heat-resistant high-functional fibers are poorly elastic and therefore lower the working efficiency of the medical and surgical workers such as physicians, surgeons and ambulance men. Accordingly, thin, elastic and tough gloves capable of being worn inside rubber gloves without detracting from the working efficiency are desired.
Heretofore, however, spun yarn is produced by spinning short fibers generally having a length of around 38 mm or around 51 mm or so, and the edges of the short fibers often protrude out of the surface of the spun yarn to form fluffs therearound. Working clothes and gloves made of spun yarn of heat-resistant high-functional fibers release the fluffs, when rubbed while they are used. Therefore, using them in clean rooms with no dust in air therein, or in painting factories in which dust, when adhered to the surfaces of painted products, detracts from the commercial value of the products is problematic. In that situation, working clothes, gloves and other fibrous products of heat-resistant high-functional fibers, which fluff little and release little dust are desired.
As described hereinabove, fibrous products of non-crimped yarn of heat-resistant high-functional fibers are unsuitable to exercises and working activities, and they fluff and release dust. In order to solve the problems, it is desired to provide heat-resistant crimped which has a good elongation percentage in stretch, a good stretch modulus of elasticity and a good appearance, not losing the excellent characteristics of good heat resistance and flame retardancy intrinsic to heat-resistant high-functional fibers, and which fluffs little and releases little dust.
To meet the requirements now in the market, various studies and proposals have been made, relating to heat-resistant crimped yarn and to a method for crimping heat-resistant high-functional fibers (Japanese Patent Laid-Open Nos. 19818/1973, 114923/1978, 27117/1991). Concretely, one proposal is to apply a method for crimping ordinary thermoplastic synthetic fibers such as nylon or polyester fibers. For example, known is a method of forcedly crimping high-elasticity fibers such as para-aramid fibers mixed with low-elasticity fibers (Japanese Patent Laid-Open No. 192839/1989). Also known is crimped yarn produced by a false-twisting method in which aramid fibers are false-twisted and crimped by the use of a non-contact heater heated at a temperature not lower than that at which the fibers begin to decompose but lower than the decomposition point of the fibers (for meta-aramid fibers, the temperature is 390° C. or higher but lower than 460° C.) , and thereafter subjected to thermal relaxation (Japanese Patent Laid-Open No. 280120/1994).
However, the known methods could not still solve all the outstanding technical problems which are how to produce high-quality crimped yarn having a good elongation percentage in stretch and a good stretch modulus of elasticity; how to prevent yarn quality deterioration, for example, tenacity reduction and color change under heat of yarn produced, and how to prevent the yarn from fluffing and from being cut or broken; and how to realize easy process control, simplification of production lines, increased productivity, and cost reduction. At present, therefore, no one has succeeded in industrial production of heat-resistant crimped yarn having a good elongation percentage in stretch and soon, not losing the physical properties intrinsic to the constituent fibers.